Application Note

Application Note
Using a DC/DC Converter with HELP4TM
and HELP3TM + Coupler Power Amplifiers
Rev 0
Relevant products
• All HELP4TM Power Amplifiers
• All HELP3TM + Coupler Power Amplifiers
HELPTM Technology
ANADIGICS’ High-Efficiency-at-Low-Power (HELPTM)
power amplifiers have selectable bias modes that
optimize efficiency for different output levels and
enable low quiescent current to reduce PA current
consumption over industry-standard transmit power
profiles to deliver significantly increased handset talk
and standby time.
The HELP4™ and HELP3™ + Coupler power
amplifiers have separate RF paths for High power and
for Medium and Low power operation. Power modes
are selected by setting the Vmode pins to a logical
high or low value as shown in Table 1. The multipath
PA design can be optimized for power, linearity and
efficiency over its full range of output power using a
fixed supply voltage, typically 3.4V. Figure 1 shows
typical performance of a HELP4™ PA in High, Medium
and Low power operating modes.
Table 1: Logic Table of Operating Mode Control for HELP4TM PA
pout
levels
BIAs
Mode
veNable
vMode1 vMode2
WCDMA - low power
(Low Bias Mode)
 +8 dBm
Low
+1.8 V
+1.8 V
WCDMA- med power
(Medium Bias mode)
7 POUT 
+16 dBM
Low
+1.8 V
WCDMA - high power
(High Bias Mode)
> +16 dBm
High
Optional lower VCC in
low power mode
 +7dBm
-
ApplIcAtIoN
Shutdown
vcc
vBAtt
+2.4 V
3.2 - 4.2 V
> 3.2 V
+1.8 V
0V
3.2 - 4.2 V
> 3.2 V
+1.8 V
0V
0V
3.2 - 4.2 V
> 3.2 V
Low
+1.8 V
+1.8 V
+1.8 V
1.5 V
> 3.2 V
Shutdown
0V
0V
0V
3.2 - 4.2 V
> 3.2 V
Icc vs pout
Figure 1: AWT6621
- ICC vs. POUT
500
25C 3.4Vcc
450
400
Icc (mA)
350
300
250
200
150
100
50
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30
pout (dBm)
10/2010
Output Power [dBm]
Using a DC/DC Converter with HELP4TM & HELP3TM + Coupler Power Amplifiers
Max Power
PA Gain Change
4dB
MPM_to_HPM
HPM_to_MPM
4dB
LPM_to_MPM
MPM_to_LPM
PA Gain Change
Input Power [dBm]
Figure 2: Output Power vs. Input Power with Gain Switching
SMPS application with HELP™ PAs
HELP™ power amplifiers are typically switched
between High and Medium Power Modes at an output
of 16 dBm or higher. Low to Mid Power switching
typically occurs around 7 dBm. Mode switching
improves the PA’s efficiency and reduces current
consumption in low/medium powers by changing
the amplifier load line working from a fixed supply
voltage.
Figure 2 illustrates the characteristics of the HELP4TM
gain switching. It suggests that the switching point
at which the PA changes from a higher gain to a
lower gain is separated by 4 dB hysteresis from the
switching point where the PA rises from a lower gain
to a higher gain. It’s recommended to implement the
hysteresis in order to avoid the PA oscilitating at the
same switching point.
levels, it is important to maintain a PA supply voltage
that allows margin to the system ACLR specification.
Often, there is enough ACLR margin at backed-off
power within each power mode that can be “traded”
for power consumption by reducing the PA collector
voltage to bring the amplifier closer to saturation.
An SMPS or DC/DC converter can be used to reduce
the collector voltage at the VCC pin of a HELP3™ or
HELP4™ PA to bring the PA closer to saturation in
the lower range of each power mode, and thereby
reduce the PA’s current consumption. In this kind of
application, Pin 10 is connected to the SMPS while
Pin 1 remains connected to Vbatt to drive the internal
voltage regulator. Figure 3 illustrates the placement
of this additional component in the PA’s application
circuit.
Because the RF system design must ensure that the
required ACLR specification is met across all power
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Application Note - Rev 0
10/2010
Using a DC/DC Converter with HELP4TM & HELP3TM+ Coupler Power Amplifiers
SMPS
VBATT
C9
GND
RFIN
C8
C10
GND
at slug
GND
C7
TX filter
L2
GND
BB
C1
C6
VBATT
VCC
RFIN
RFOUT
VMODE2
CPL IN
VMODE1
GND
VEN
C2
GND
GND
C4
C3
RFOUT
Duplexer
L1
50Ω
CPLOUT
GND
GND
GND
To
Detector
PA_R1
PA_R0
PA_0N
C5
GND
Figure 3: Typical Application Circuit with SMPS
Application Note - Rev 0
10/2010
3
Using a DC/DC Converter with HELP4TM & HELP3TM + Coupler Power Amplifiers
Figure 4 shows typical ACLR performance of a
HELP4TM PA in this application. Note that, in the lower
portion of the High Power Mode, the PA collector
voltage (VCC) can be reduced below 3.4 V without
failing a minimum ACLR requirement. Similar data was
collected for the Mid Power Mode (Figure 5) and the
Low Power Mode (Figure 6).
AWt6621: HpM Acp at reduced vcc
Figure 4: AWT6621- HPM ACLR Measured at Reduced VCC
-30
-32
VCC=3.1 V
-34
VCC=3 V
VCC=2.9 V
Acp (dBc)
-36
VCC=2.8 V
-38
VCC=2.7 V
-40
VCC=2.6 V
VCC=2.5 V
-42
VCC=2.4 V
-44
VCC=2.3 V
-46
VCC=2.2 V
VCC=2.1 V
-48
VCC=2.0 V
-50
15
17
19
21
23
pout (dBm)
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Application Note - Rev 0
10/2010
25
27
Using a DC/DC Converter with HELP4TM & HELP3TM+ Coupler Power Amplifiers
AWt6621: MpM Acp at reduced vcc
Figure 5: AWT6621- MPM ACLR Measured at reduced VCC
-25
VCC=3.1 V
VCC=3 V
-30
VCC=2.9 V
VCC=2.8 V
Acp (dBc)
-35
VCC=2.7 V
VCC=2.6 V
-40
VCC=2.5 V
VCC=2.4 V
-45
VCC=2.3 V
VCC=2.2 V
-50
VCC=2.1 V
VCC=2.0 V
-55
5
7
9
11
13
15
17
19
pout (dBm)
AWt6621: lpM Acp at reduced vcc
Figure 6: AWT6621- LPM ACLR Measured at reduced VCC
-25
VCC=3.1 V
VCC=3 V
VCC=2.9 V
-30
Acp (dBc)
VCC=2.8 V
VCC=2.7 V
-35
VCC=2.6 V
VCC=2.5 V
-40
VCC=2.4 V
VCC=2.3 V
VCC=2.2 V
-45
VCC=2.1 V
VCC=2.0 V
-50
0
2
4
6
pout (dBm)
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Application Note - Rev 0
10/2010
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5
Using a DC/DC Converter with HELP4TM & HELP3TM + Coupler Power Amplifiers
Because HELP™ architecture is designed to improve efficiency at low and medium powers, and because ACLR
and gain change between power modes, the greatest benefit of using a SMPS with a HELP4™ or HELP3™
plus Coupler PA is found in High Power mode. If a reduced supply voltage is available, a “fourth” power mode
can be created from a lower power portion of HPM, as shown in Figure 7.
600
Figure 7: Power Mode Switching in a HELP4TM PA with SMPS
550
Battery Current Consumption (mA)
500
AWT6621 HPM
Test Conditions:
AWT6621 HELP4™ PA
WCDMA (R99) Waveform
Battery supply at 3.4V
SMPS provides 2.4V with 95% efficiency
450
400
AWT6621 HPM with SMPS
AWT6621 MPM
AWT6621 LPM
350
300
SMPS switch at 24dBm
250
200
150
100
HPM/MPM switch at 16dBm
MPM/LPM switch at 7dBm
50
0
-5
0
5
10
15
20
25
30
PA Output (dBm)
The benefit of reducing VCC in this way can be seen by calculating the average current consumption over
a standard power profile like DG09. Assuming high efficiency in the SMPS or DC/DC converter, reducing
the supply voltage to a HELP4™ PA like AWT6621 in the lower power portion of HPM provides a 10 – 15%
reduction in battery current, as shown in Table 2. Reducing the supply voltage to a HELP3™ plus Coupler PA
like AWU6601 has a similar benefit.
Table 2: Improved Current Consumption over DG09 Profile
6
technology
power Amplifier
Quiescent
current
Average
over dG09
HELP3TM + Coupler
AWU6601 at 3.4 V
8.0
30.1
HELP3TM + Coupler
with SMPS
AWT6601 with SMPS at 2.4 V
for Iqc and some HPM
6.2
26.7
HELP4TM
AWT6621 at 3.4 V
1.8
21.4
HELP4TM with SMPS
AWT6621 with SMPS at 2.4 V
for Iqc and some HPM
1.4
18.7
Application Note - Rev 0
10/2010
Using a DC/DC Converter with HELP4TM & HELP3TM+ Coupler Power Amplifiers
Additional benefits in average current consumption can be obtained by operating the SMPS from a battery
voltage above 3.4V and by using the SMPS to reduce Vcc in the lower power portions of the Medium and Low
Power Modes as well as the High Power Mode. Careful adjustment of Vcc over the entire range of the DG09
power profile has been shown to reduce average current as much as 50%. Consult ANADIGICS Applications
Engineering for advice on your application.
GAIN vs. FREQUENCY
The PA gain is a function of frequency. At the same
time, the Gain vs. Frequency response may vary at
the different power levels. Figure 8 shows an example
of Gain vs. Frequency response for AWT6621,
at each power mode. Variation of gain over the
band in each power mode must be considered when
using a DC/DC converter or SMPS to regulate the
PA supply.
Figure 8: Variation of PA Gain vs Frequency
30
HpM, pout = 28.5dBm
MpM, pout = 17dBm
lpM, pout = 8dBm
25
Gain (dB)
20
15
10
5
0
1920
1930
1940
1950
1960
1970
1980
Frequency (MHz)
Application Note - Rev 0
10/2010
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Using a DC/DC Converter with HELP4TM & HELP3TM + Coupler Power Amplifiers
Gain vs TEMPERATURE
The PA gain changes as a function of temperature. It
can be seen from Figure 9 that AWT6621 HPM gain
varies approximately 3 dB over a temperature range
of 100 degrees (from -10 8C to +90 8C). The effect
of gain offset over temperature can be pronounced in
ILPC test, around the gain switching point. If the PA
is calibrated in LPM first and then move up to MPM
and HPM, it may experience problems in ILPC step
E. Likewise, if the PA is calibrated from HPM to LPM,
it might see a problem in ILPC step F. Adjustments
to temperature compensation parameters may be
necessary to offset changes in gain step size when
using a DC/DC converter or SMPS to control the PA
in different power mode states.
AWt6621 HpM Gain (dB), 1950MHz
Figure 9: AWT6621, Gain in HPM at 3 Temperatures
30
25C 3.4Vcc
29
-30C 3.4Vcc
90C 3.4Vcc
28
Gain (dB)
27
26
25
24
23
22
21
20
0
2
4
6
8
10
12
14
16
18
20
22
24
pout (dBm)
Recommended PA turn-on and turn-off sequences
Refer to Figure 10 for recommended system level power up/down sequence.
Figure 10: Recommended Turn-On/Off Sequence
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Application Note - Rev 0
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28
30
32
Using a DC/DC Converter with HELP4TM & HELP3TM + Coupler Power Amplifiers
ANADIGICS, Inc.
141 Mount Bethel Road
Warren, New Jersey 07059, U.S.A.
Tel: +1 (908) 668-5000
Fax: +1 (908) 668-5132
URL: http://www.anadigics.com
IMPORTANT NOTICE
ANADIGICS, Inc. reserves the right to make changes to its products or to discontinue any product at any time without notice.
The product specifications contained in Advanced Product Information sheets and Preliminary Data Sheets are subject to
change prior to a product’s formal introduction. Information in Data Sheets have been carefully checked and are assumed
to be reliable; however, ANADIGICS assumes no responsibilities for inaccuracies. ANADIGICS strongly urges customers
to verify that the information they are using is current before placing orders.
warning
ANADIGICS products are not intended for use in life support appliances, devices or systems. Use of an ANADIGICS product
in any such application without written consent is prohibited.
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Application Note - Rev 0
10/2010